Jacqueline Bouvier Kennedy Onassis is not the frail, whispery-voiced woman the American people saw standing by the side of President Kennedy, says the author of an unauthorized biography of the former first lady.

The real Jackie, says writer C. David Heymann, is a strong-willed woman who was probably a principal designer of the Kennedy administration's Camelot image."The image of this good Catholic husband with two beautiful children and a beautiful wife posing on the White House lawn was not the case," he said.

In his book, "A Woman Named Jackie," which went on sale Tuesday, Heymann attempted to unravel the life and character of one of the world's most admired, photographed and written-about yet enigmatic women.

"Although there have been so many things written about her, nothing I read really did the woman justice," he said in a telephone interview. "Everything was based on gossip and innuendo. I felt something along definite lines should be written."

His 631-page book is based on interviews with 825 people, including friends, employees and family members, but none of the Kennedys.

The author, by appealing to the director of Presidential Libraries in Washington D.C., gained access to the former first lady's White House social files. Through the Freedom of Information Act, he obtained thousands of pages of previously undisclosed FBI, CIA and Secret Service files.

Heymann's purpose was not to document the public successes and failures of the Kennedys' years in the White House, but to scrutinize their successes and failures as individuals - as husband and wife.

Indeed, a good portion of the book is devoted to the slain president's many alleged liaisons with women.

"A lot of this wasn't my original intention to go into his affairs in such depth," said Heymann. "I had merely heard all the rumors and innuendoes. But, as a result of digging into various files . . . a lot of this became fact not merely rumor."

Onassis' spokeswoman, Nancy Tuckerman, has said Onassis would not comment on the book. A telephone message left at her office Tuesday was not returned.

According to Heymann, Kennedy once sneaked out of a New York hotel for a sexual liaison without telling the Secret Service and without taking the list of codes he needed in the event of a nuclear attack.